You could start by checking the motor itself. If you have a ohmmeter, check resistance between the + terminal which is on the left, and the - which is on the right. There are marks on the motor, so you can't get confused. There should be no resistance. If there is, try checking the middle terminal which is also a positive, to the - terminal. If there is no resistance there, you could just swap the green positive wire which is on the left of your connector pigtail, to the central position. Your fan should now work.